1use smallvec::SmallVec;
2use taffy::style::{Display, Position};
3
4use crate::{
5 point, AnyElement, Bounds, Element, ElementContext, IntoElement, LayoutId, ParentElement,
6 Pixels, Point, Size, Style,
7};
8
9/// The state that the anchored element element uses to track its children.
10pub struct AnchoredState {
11 child_layout_ids: SmallVec<[LayoutId; 4]>,
12}
13
14/// An anchored element that can be used to display UI that
15/// will avoid overflowing the window bounds.
16pub struct Anchored {
17 children: SmallVec<[AnyElement; 2]>,
18 anchor_corner: AnchorCorner,
19 fit_mode: AnchoredFitMode,
20 anchor_position: Option<Point<Pixels>>,
21 position_mode: AnchoredPositionMode,
22}
23
24/// anchored gives you an element that will avoid overflowing the window bounds.
25/// Its children should have no margin to avoid measurement issues.
26pub fn anchored() -> Anchored {
27 Anchored {
28 children: SmallVec::new(),
29 anchor_corner: AnchorCorner::TopLeft,
30 fit_mode: AnchoredFitMode::SwitchAnchor,
31 anchor_position: None,
32 position_mode: AnchoredPositionMode::Window,
33 }
34}
35
36impl Anchored {
37 /// Sets which corner of the anchored element should be anchored to the current position.
38 pub fn anchor(mut self, anchor: AnchorCorner) -> Self {
39 self.anchor_corner = anchor;
40 self
41 }
42
43 /// Sets the position in window coordinates
44 /// (otherwise the location the anchored element is rendered is used)
45 pub fn position(mut self, anchor: Point<Pixels>) -> Self {
46 self.anchor_position = Some(anchor);
47 self
48 }
49
50 /// Sets the position mode for this anchored element. Local will have this
51 /// interpret its [`Anchored::position`] as relative to the parent element.
52 /// While Window will have it interpret the position as relative to the window.
53 pub fn position_mode(mut self, mode: AnchoredPositionMode) -> Self {
54 self.position_mode = mode;
55 self
56 }
57
58 /// Snap to window edge instead of switching anchor corner when an overflow would occur.
59 pub fn snap_to_window(mut self) -> Self {
60 self.fit_mode = AnchoredFitMode::SnapToWindow;
61 self
62 }
63}
64
65impl ParentElement for Anchored {
66 fn extend(&mut self, elements: impl Iterator<Item = AnyElement>) {
67 self.children.extend(elements)
68 }
69}
70
71impl Element for Anchored {
72 type RequestLayoutState = AnchoredState;
73 type PrepaintState = ();
74
75 fn request_layout(
76 &mut self,
77 cx: &mut ElementContext,
78 ) -> (crate::LayoutId, Self::RequestLayoutState) {
79 let child_layout_ids = self
80 .children
81 .iter_mut()
82 .map(|child| child.request_layout(cx))
83 .collect::<SmallVec<_>>();
84
85 let anchored_style = Style {
86 position: Position::Absolute,
87 display: Display::Flex,
88 ..Style::default()
89 };
90
91 let layout_id = cx.request_layout(&anchored_style, child_layout_ids.iter().copied());
92
93 (layout_id, AnchoredState { child_layout_ids })
94 }
95
96 fn prepaint(
97 &mut self,
98 bounds: Bounds<Pixels>,
99 request_layout: &mut Self::RequestLayoutState,
100 cx: &mut ElementContext,
101 ) {
102 if request_layout.child_layout_ids.is_empty() {
103 return;
104 }
105
106 let mut child_min = point(Pixels::MAX, Pixels::MAX);
107 let mut child_max = Point::default();
108 for child_layout_id in &request_layout.child_layout_ids {
109 let child_bounds = cx.layout_bounds(*child_layout_id);
110 child_min = child_min.min(&child_bounds.origin);
111 child_max = child_max.max(&child_bounds.lower_right());
112 }
113 let size: Size<Pixels> = (child_max - child_min).into();
114
115 let (origin, mut desired) = self.position_mode.get_position_and_bounds(
116 self.anchor_position,
117 self.anchor_corner,
118 size,
119 bounds,
120 );
121
122 let limits = Bounds {
123 origin: Point::default(),
124 size: cx.viewport_size(),
125 };
126
127 if self.fit_mode == AnchoredFitMode::SwitchAnchor {
128 let mut anchor_corner = self.anchor_corner;
129
130 if desired.left() < limits.left() || desired.right() > limits.right() {
131 let switched = anchor_corner
132 .switch_axis(Axis::Horizontal)
133 .get_bounds(origin, size);
134 if !(switched.left() < limits.left() || switched.right() > limits.right()) {
135 anchor_corner = anchor_corner.switch_axis(Axis::Horizontal);
136 desired = switched
137 }
138 }
139
140 if desired.top() < limits.top() || desired.bottom() > limits.bottom() {
141 let switched = anchor_corner
142 .switch_axis(Axis::Vertical)
143 .get_bounds(origin, size);
144 if !(switched.top() < limits.top() || switched.bottom() > limits.bottom()) {
145 desired = switched;
146 }
147 }
148 }
149
150 // Snap the horizontal edges of the anchored element to the horizontal edges of the window if
151 // its horizontal bounds overflow, aligning to the left if it is wider than the limits.
152 if desired.right() > limits.right() {
153 desired.origin.x -= desired.right() - limits.right();
154 }
155 if desired.left() < limits.left() {
156 desired.origin.x = limits.origin.x;
157 }
158
159 // Snap the vertical edges of the anchored element to the vertical edges of the window if
160 // its vertical bounds overflow, aligning to the top if it is taller than the limits.
161 if desired.bottom() > limits.bottom() {
162 desired.origin.y -= desired.bottom() - limits.bottom();
163 }
164 if desired.top() < limits.top() {
165 desired.origin.y = limits.origin.y;
166 }
167
168 let offset = desired.origin - bounds.origin;
169 let offset = point(offset.x.round(), offset.y.round());
170
171 cx.with_element_offset(offset, |cx| {
172 for child in &mut self.children {
173 child.prepaint(cx);
174 }
175 })
176 }
177
178 fn paint(
179 &mut self,
180 _bounds: crate::Bounds<crate::Pixels>,
181 _request_layout: &mut Self::RequestLayoutState,
182 _prepaint: &mut Self::PrepaintState,
183 cx: &mut ElementContext,
184 ) {
185 for child in &mut self.children {
186 child.paint(cx);
187 }
188 }
189}
190
191impl IntoElement for Anchored {
192 type Element = Self;
193
194 fn into_element(self) -> Self::Element {
195 self
196 }
197}
198
199enum Axis {
200 Horizontal,
201 Vertical,
202}
203
204/// Which algorithm to use when fitting the anchored element to be inside the window.
205#[derive(Copy, Clone, PartialEq)]
206pub enum AnchoredFitMode {
207 /// Snap the anchored element to the window edge
208 SnapToWindow,
209 /// Switch which corner anchor this anchored element is attached to
210 SwitchAnchor,
211}
212
213/// Which algorithm to use when positioning the anchored element.
214#[derive(Copy, Clone, PartialEq)]
215pub enum AnchoredPositionMode {
216 /// Position the anchored element relative to the window
217 Window,
218 /// Position the anchored element relative to its parent
219 Local,
220}
221
222impl AnchoredPositionMode {
223 fn get_position_and_bounds(
224 &self,
225 anchor_position: Option<Point<Pixels>>,
226 anchor_corner: AnchorCorner,
227 size: Size<Pixels>,
228 bounds: Bounds<Pixels>,
229 ) -> (Point<Pixels>, Bounds<Pixels>) {
230 match self {
231 AnchoredPositionMode::Window => {
232 let anchor_position = anchor_position.unwrap_or(bounds.origin);
233 let bounds = anchor_corner.get_bounds(anchor_position, size);
234 (anchor_position, bounds)
235 }
236 AnchoredPositionMode::Local => {
237 let anchor_position = anchor_position.unwrap_or_default();
238 let bounds = anchor_corner.get_bounds(bounds.origin + anchor_position, size);
239 (anchor_position, bounds)
240 }
241 }
242 }
243}
244
245/// Which corner of the anchored element should be considered the anchor.
246#[derive(Clone, Copy, PartialEq, Eq)]
247pub enum AnchorCorner {
248 /// The top left corner
249 TopLeft,
250 /// The top right corner
251 TopRight,
252 /// The bottom left corner
253 BottomLeft,
254 /// The bottom right corner
255 BottomRight,
256}
257
258impl AnchorCorner {
259 fn get_bounds(&self, origin: Point<Pixels>, size: Size<Pixels>) -> Bounds<Pixels> {
260 let origin = match self {
261 Self::TopLeft => origin,
262 Self::TopRight => Point {
263 x: origin.x - size.width,
264 y: origin.y,
265 },
266 Self::BottomLeft => Point {
267 x: origin.x,
268 y: origin.y - size.height,
269 },
270 Self::BottomRight => Point {
271 x: origin.x - size.width,
272 y: origin.y - size.height,
273 },
274 };
275
276 Bounds { origin, size }
277 }
278
279 /// Get the point corresponding to this anchor corner in `bounds`.
280 pub fn corner(&self, bounds: Bounds<Pixels>) -> Point<Pixels> {
281 match self {
282 Self::TopLeft => bounds.origin,
283 Self::TopRight => bounds.upper_right(),
284 Self::BottomLeft => bounds.lower_left(),
285 Self::BottomRight => bounds.lower_right(),
286 }
287 }
288
289 fn switch_axis(self, axis: Axis) -> Self {
290 match axis {
291 Axis::Vertical => match self {
292 AnchorCorner::TopLeft => AnchorCorner::BottomLeft,
293 AnchorCorner::TopRight => AnchorCorner::BottomRight,
294 AnchorCorner::BottomLeft => AnchorCorner::TopLeft,
295 AnchorCorner::BottomRight => AnchorCorner::TopRight,
296 },
297 Axis::Horizontal => match self {
298 AnchorCorner::TopLeft => AnchorCorner::TopRight,
299 AnchorCorner::TopRight => AnchorCorner::TopLeft,
300 AnchorCorner::BottomLeft => AnchorCorner::BottomRight,
301 AnchorCorner::BottomRight => AnchorCorner::BottomLeft,
302 },
303 }
304 }
305}